Electric tube



3am 1% 19 35 u FUNARQFF 2,357,570

ELECTRIC TUBE Filed July 8, 1943 49 INVENTOR [g v .50 4' 4 6 J1 ATTORNEYtioned with an electrode lace area or electric resistance is virtuallynot Patented Jan. 16, 1945 ELECTRIC TUBE Urie Funaroif, Bloomfield, N. Jassignor to Westinghouse Electric East Pittsburgh, vania & ManufacturingCompany, Pa.', a corporation of Pennsyl- Application July 8, 1943,Serial No. 493,887

Claims.

This invention relates to electric devices for measuring, receiving,amplifying or control purposes in general, and in one of its moreparticular aspects to measuring tubes or pressure gauges of the Piranitype.

In Pirani gauges, a vessel or tube envelope having a conduit forsupplying the pressure to be determined contains an electrode orconductor filament which is exposed to the tube atmosphere and, when inoperation, is traversed and heated by electric current. The resistanceof the electrode or filament varies in dependence upon the dissipationof heat through the tube atmosphere. Since this diss'pation is dependentupon the gas pressure, the resistance of the filament is a measure ofthe pressure magnitude to, be

determined.

For accuracy and high speed of response, it is often desirable to use insuch and other electric devices an-electrode or conductive filamentwhich offers maximum surface and maximum electrical limited by the prior"art dimensional requirements imposed by the necessary mechanicalstrength,

V stability and ruggedness of construction.

An object, allied to the-foregoing, is to provide such a device with anelectrode or filament which contains a large efiective surface area anda high resistance together with high mechanical strength and stabilityand at a minimum of thickness and thermal mass. According to the priorart, some of these desirable characteristics appear contradictory. Inparticular, the available surface area, electrical resistance, minimumthickness and minimum mass have heretofore been limited by the need forsuflicient mechanical strength and ruggedness of construction. Anotherlimiting factor in measuring and control devices of this kind,especially in previous gauges of the Pirani type. has been the necessityof maintaining a constant characteristic and a coristant zero point ofthe electrode or filament circuit. As a result, the known Pirani gaugeshave had a rather limited accuracy, have been nonuniform and havepossessed a relatively high time constant oi response. p

In one of the known Pirani gauges, the filament is composed of a corewire of a mechanically strong butchemically active metal, such astantalum, with a coating of a mechanically less resistant but chemicallyinert metal, such as platinum. However, the maximum surface and themaximum pressure or temperature-responsive resistance of such a coatedmetal filament are also limited by the lowest permissible strength andsize of the conducting metal core, and the core metal. is apt to oxidizebelow the coating. especially at high temperature.

It is an object of the present invention to' provide an electric deviceof the types aforemenor filament whose surmeans. The coating may be madeof platinum,

total electrical resistance together with high mechanical strength inproportional degrees not obtainable with the known tube and filamentconstructions.

Another object-of the invention is to provide an electrode or filamentin measuring tubes, for instance of the Pirani gauge type, which ofiersan increased sensitivity and speed of response in conjunctionwith'astable characteristic and zero point.

A further object related to the one just mentioned is to increase theeffective surface area of a tube electrode .or filament whilemaintaining a high total electrical resistance and a high e1ectricalandmechanical stability.

According to the invention and for achieving the foregoing objects, theactive electrode or filament of an electric device as abovecharacteriz'ed is composed of a body or base of insulating material anda coating disposed on the insulating body and consisting of the activeconductive material. The insulating body consists preferably of amaterial capable of withstanding the operating temperature of theconductive coating without appreciably afiecting the characteristic ofthe filament. Heat-resistant or highly refractory inorganicsubstancessuch as mica, alundum, lava, and quartz are especiallysuitable for this purpose, although glass and glass wool ribbons canalso be used at most operating temperatures.

The conducting coating or film is'secured to the surface of theinsulator by sputtering, spraying, electroplating, mirrorplating orother suitable iridium, or other material suitable for Pirani gauges orother electric vacuum tubes. Its resistance is adjusted to suit thedesired purpose or characteristics by omitting, scratching or cuttingaway parts of the surface film as well as by properly selecting thethickness of the film or coating.

To secure maximum surface and minimum thermal. mass of the insulatingbase, said base may be made in fiat sheets, fine strands, threads orribbons, arranged, corrugated, spiralled, wound as a helix, folded inaccordion shape or otherwise, and mounted or connected in multiple orseriesunits if desired. The invention will be more fully understoodfilaments or electrodes for electric devices according to the invention;and

Fig. 8 is a perspective and partly sectional view of a resistorarrangement for measuring determinants of fluid flow, the measuringresistors consisting of filaments or electrodes as disclosed by thisinvention.

Referring to Fig. 1, reference numeral I indicates the envelope of aPirani measuring tube. The envelope is attached at its lower end to abase 2 and at its upper end is shown as-having a tubular conduit 3 forsupplying the atmosphere whose pressure is to be measured. The envelopeI, while indicated as comprised of glass, may be of metal, or othermaterial, and preferably has a substantially cylindrical, elongatedshape. .Its axial-end, for convenience denominated as the lower end andopposite to the supply conduit 3,

likewise for convenience of description referred to as the upper'end, isformed with a reentrant stem and press 4. A central holder 5, preferablycomprised of a glass rod, is mounted on the press 4 and extends upwardlytherefrom coaxial with the envelope. A plurality of arms, here shown asfour in number, 6, I, 8 and 9, radiate from and are carried by theholder next its upper end, said arms being disposed at right, angles toone another and in a common plane transverse to the holder. These armsserve to secure the electrode or filament sections in proper position.

Two lead-in wires III and II from outside terminals I2, II at theunderface of the base, extend upwardly within the press 4 and projectabove the press on opposite sides of the holder. The electrode orfilament structure-is suspended from said radial arms and-comprises asmany sections as there are arms. The present showing provides foursections marked II, II, "and I1, respectiv'ely. A bottom marginalportion of one section I4 has a connector ll applied on one face of thesaid section and a bottom marginal portion of a next adjacent section I!has a connector Is one face of said adjacent section looking toward thefirst said face. These connectors I8 and I! are welded, soldered, orotherwise securadzto upper ends of said leads I II and I I.

It is desired to provide a long path for the current traversing thefilament from one lead-in wire'- to the other. Understandingofaccomplishment of this desideratum will follow more readily from adescription of the filament structure. Generally speaking, each of theopposite faces of each section is an electrically conductive surfacedistinct from. the eiectricalconductiye surface on the other face of thesection: Each filament-section consists of an insulating body or base 20which is preferably in the form of a strip or sheet according to Fig. 3,and which is covered on opposite faces, but not around the edges, by avaristor coating of conductive material, thereby providing each filamentsection with filament portions 2|, 22 on opposite faces of the body 20.The coating material consists of electronically or electricallyeffective substance and may be applied by dipping, sputtering, spraying,painting, lating, or other acceptable manner. In a'Pirani gauge, asillustrated in Fig. 1, a, chemically inert metal, such as platinum,iridium or an alloy thereof, is preferably applied as the varistorcoating. It will be understood by those skilled in the art that avaristor material is'one which has a change of characteristic, usually aresistance characteristic resultant from being exposed to heat, light,pres sure or other condition. Since the electrode or filament of thespecific structure being described should withstand relatively hightemperatures, the non-conducting base 20 is preferably made of arefractory material such as mica, steatite, lava, alundum, or quartz.

In order to prolong the electric path of the filament surface, filamentportions or coatings 2I and 22 are omitted, Scratched, or cut away atappropriate locations for the purpose. For instance, filament surfaceseparation is shown lc-ngitudinal of the filament section intermediateof the side edges from the bottom and up'to a short distance from thetop of the section so that narrow strips 23 and 24 on both margins ofthe filament body are free of conducting'material and bisect theconductive surface for most of its length. As a result, each filamentsection forms a conducting path on the faces thereof having the generalform of an inverted U, by which the conducting path extends upward atone longitudinal margin of the surface of the insulating body, crossesto the opposite margin and then proceeds downward at the said oppositemargin to the bottom end thereof, thus resulting in an effective doublelength of path of about double the length of the body on one face of thebody. A like double-length of path is provided on the other face of saidsection. For convenience in reference, the filament area on the marginnearest the structure supporting post or holder 5 will be referred to asthe inner leg of the filament portion and the area on the far side ofthe nonconductive strip more distant, from the said post will betermedthe outer leg of the filament These two leg areas connect at their upperends by an area which will b referred to asthe file ment hip.

The bottom of the outer filament leg on one face of the insulating bodyis'connected to the bottom of. the outer filament leg on the oppositeface of said body by means of a u-shaped clip 25, or other means,passing under the end of said body from the leg of one filament portionto the corresponding leg of the other filament portion.

' The inner filament legs, however, each preferably'have individualstrip-like connectors of which two, identified by numerals I8 and I9have been referred to above, and the others of which are now identifiedby numeral 26. There is no direct connection between the connector onone face of the insulator body with the con- *nector on the reverse facethereof, but the connector 26 on one insulating body is ioinedwith thenext succeeding connector on the next insulating body, by means of aconductor 21 shown in Fig. 2 asl a short wire bent at a right angle andsituated with its legs cross-wise of the filament and longitudinally ofthe connector, and sel the exterior terminal I2 through lead III curedthereto by welding or otherwise. Consequently, an electric current pathextends from nector I8, thence upthe inner leg, across the "hip and downthe outer leg of filament portion 2| of filament'portion I4, nector 25under and to t hence by way of cone opposite face of the to consulatingbody insulating body; up the outer leg and down the inner leg of thatportion l of the same section l4, thence over conductor 21 to the nextsection l4, through the full length of filament portions 2|, 22 onopposite sides of that section, and similarly to and through successiveconductors 21 and sections the full length of filament portions 2|, 22thereof, and then to the lead H and the exterior terminal I3. a

In order that the several filament sections may be supported attheirupper ends-without shortcircuiting from portion 2| thereof on oneface of the body' to the portion 22 o the other'face the body is freeeoffilament coating or material for a marginal depth 28 and suitable clips29 are ap-. plied at those margins adequately secured, as by grippingand frictional engagement of the in- Tabs or ears 3!! stamped from theseclips form a means by which the clips may be welded or otherwise securedto the arms 6, I, 8

and 9.

In operation, an electric measuring circuit is connected to theterminals 12 and I3 so as to measure either the resistance of theabove-described current path or the voltage or. current in the measuringcircuit as determined by the resistance magnitude of this path. Due toits connection at 3 with an atmosphere, for instance, a low vacuum tobemeasured, the dissipation of heat from the sixteen filament legs of theeight filament portions of the four filament sections of the electrodethrough the inner tube atmosphere depends on the thermal conductivity ofthe tube atmosphere and hence on the pressure to be determined. As a'result, the measured magnitude of the gauge resistance, voltage orcurrent is a measure of the pressure magnitude. specific number ofsections, portions and legs have been shown and recited for clarity, itis to be understood in practice that the number may be otherwise asfound desirable or necessary.

The modification of an, electrode or filament arrangement illustrated inFig. 4 is of the selfsupporting type. The electrode consists of a thincylindric sleeve 29 of insulating material whose inner and outersurfaces are covered byconducting filamentary varistor coatings orportions 30 and 3|, respectively. When using this structure in a Piranigauge, the coating consists of platinum or the like chemically inertmetal as heretofore mentioned. By omitting or cutting away part of thecoating along a helical line so as to form a non-conductive path, eachportion is divided into a winding of conducting material. A terminal orlead 32 is attached to the lower end of the outside conducting strip orportion'3l, and another lead v33 is attached to the lower end of theinside conductive strip or portion. .A connector 33 is applied over theupper edge of the electrode structure so as to electrically connect theupper convolutions of the windings of the filament portions 30,- 3|.

The two'leadsj l and 33also constitute mounting means for the selfesupporting electrode structure. It will be seen that in an electrode orfilament construction of this type, the electric current passes inseries first through the entire length of one helical portion thereof,thence through the connector to the other helical portion and throughthe entire length of the last-mentioned helical portion.- The 'top andbottom edges of the insulating body are "free of conductive 'materialseas to avoid, short- .circuitlngthereat. v I

According to the embodimentpf Fig.- 5 which While a a is also of theself-supporting type, a substantially helical insulating body or strip34 is-covered at one or both surfaces with conducting and electricallyeffective varistor material and is attached 5 to two leads and mountingmeans 35 and 36,. so

that the electric measuring or heating current passes from lead 35through the entire length of the coating on strip 34 to the other lead36. Since the leads 3s, as are shown attached to the inner surfaceportion of the helically wound strip, the current passes through thatportion. To also use the outer surface portion, the filamentary materialis also appliedaround the edges of the strip or the ends thereof.

The embodiment shown in Fig. 6 contains an accordion-shaped strip orbody member 34' of insulating material which is coated on one or bothsideswith a temperature-responsive or otherwise electrically effectivevaristor material of the type and for the purposes above described. Thestrip (or body 34 is attached to lead wires 35' and 36, which serve alsoas mounting means for connecting the coating with a measuring oroperating circuit. Here again, for use of both surface portions of thefilament material, the said material is applied around the ends of thestrip or around the side edges or otherwise as found most expedient ordesirable.

metallic filamentary varistor coating is applied to a rectangular flatplate or body- 31 of n0n-con ducting material. The coating consists of ametallic film or deposit so arranged as to extend in the followingmanner.- The conductive path begins at a metal connector 38 attached toa lead wire and mounting means 39 and extends upward along an upwardlyextending strip or filament portion 40. At the upper end, the filamentportion 40 is connected over the,upper edge of 40 the insulating basewith a similar strip or portion of coating located at the rear surfaceof the plate 31" and depending tothe bottom of said base to constitute afilament section. Another conducting filament section 4| extendslikewise over both the front and rear surfaces of the base or plate 31,the rear and lower ends of said sections having ahip connection, whereasthe lower front end of said second section 4! has a hip connection 42with a third conducting section 43 similar to the first one 40. Theupper end of section 43 has a connector 44 attached thereto which inturn is attached to a central lead and holder 45. The lower rear end ofsection 43 has a hip connection with the lower rear end of a fourthsee-- as tion whose lower front end has a hip connection 41 with a fifthconducting section 48. The lower I rear end of section 48 has aconnector 49 attached thereto which in turn is connected to a leadand'supporting means 50. -The three leads 0 and supporting means 39; 45and 50 are mounted on the stem portion 5I of a tube envelope similar tothe stem 4 and envelope I shown in Fig. 1. By appropriate circuitconnections 52, 53 and 54 from leads 39, 45 and 50 respectively througha special double-blade switch 55, '56, current from a supply line 51, 58may be passed as desired in series through the several filament sectionsor in parallel through the two halves thereof.

When-the leads 39,;45 and Silare properly connected to anelectriclieating and measuring circuit, represented by supply lines 51,58 as with the switch blades in dotted linerposition, the cur- 6 rentflows from lead 45 through one-half of the filament sections to lead 39,and also through the 7 other hair of. the filament sections to lead 50.

pressur ranges or sensitivity, etc.

The operation of the electrode constructions shown in Figs. 4 through'7, when applied to a Pirani gauge, is in principle similar to theabovedescribed operation of the tube shown in Fig. 1.

The main advantage of such plated-insulators over the known filaments isthat the maximum" various electronic tubes. For example, in aphotoelectric cell or photo-glow tube, a metal of high surfaceresistance or thinness are no longer limited by the strength of theconducting material, but can be made as large as the size of the tubepermits and as thin as feasible. The fact that conducting varistormaterialcan be deposited by piatinir. spraying, and otherwise, permitsmaking the filament about 10 to 100 times thinner than previouslypossible and, thus for a given surface area for the filament per unit oflength of current path, as well as by permitting use of increasedfilament length, affords greater resistance in the same tube space orunit volume than was previously possible.

Other advantages of such filaments are that 'a weak conducting materialcan be used without any danger that a force acting on it tends tostretch or break the filament proper or make it sag and change inlength'and resistance. The conducting filament unit is also preventedfrom changes caused by its own weight. By virtue of thesepropertieahigher flashing, baking and operating temperatures canbe,used. As a result,

the filament is degassed more thoroughly and quickly and assumes moreuniform and desirable characteristics, without dangerously weakening orinjuring the filament structure or shortening the life of the tube, anachievement not attainable by prior art constructions. Moreover, thefilament or electrode retains this uniformity and initial characteristicfor a much longer time. The large surface can be fixed veryaccuratelymerely by keeping the easily measurable overall large dimensions of theinsulator very accurate without being affected appreciably by variationsin thickness of either conducting or insulator material. The initialresistance can easily be kept within limits of accuracy of themeasuringinstruments used, by scratching lines in the conducting surfaceuntil the desired resistance is obtained, or by controllingthe'conductor's thickness or resistance in any other suitable manner.Thelarge magnitudes of surface and resistance possible with such coatedfilaments renders non-uniformities in the manner of attaching, clamping,or welding supports. clamps and leads, and variations in the size orthickness of these auxiliary elements relatively smaller so that themagnitude of such non-uniformities becomes as a rule negligible. Theseadvantages and the absence of fragile materials facilitate manufacturingthese articles in accordance with desired initial characteristics andwith much greater accuracy, higher degree of uniformity, and much. lessshrinkage than hitherto possible. This also reduces or eliminates therequirements of calibrating each tube or matching pairsoftubes.

Such plated or otherwise coated insulator-filaments also lendthemselveslrfiore readily to other uses, such as directly heatedlarge-surfaced hot cathodes, anodes or electron-emitting plates in workfunction but better physical characteristics as to permanence,destructibility, or volatility, than potassium or other usual metals,can be used if plated on an insulating base and heated by an auxiliaryfilament current to a point where the energy or work, necessary to pullan electron out of the plate, is decreased by the raised temperature tothe desired operating value or voltage.

Fig. 8 represents a case in which the invention is applied to a pair oftemperature-responsive resistors for measuring a rate of cooling or rateof flow. The resistors consist of substantially U-shaped strips 'II and12, each containing an insulating base coated with thermo-responsiveresistance varistor material. The strips are arranged in substantiallythe same plane fill .the past.

within a tube II which forms part of a conduit system for conducting afluid stream whose rate of flow or rate of cooling or heating is to bemeasured. The location of the resistors is substantially central to theflow lines so that the fluid passes first along one and then along theother resistor affecting their respective resistance r values independence upon the local temperature or thermal conductivity of thefiuid. Each resistor is. attached to a pair of terminals", II and l, 11,respectively,-for connecting them to -a measuring circuit (not shown) inorder to desible to measure very small differences in temperature orthermal conductivity and hence permits placing the two resistors muchcloser togetherthan heretofore possible. As a result, the

invention in this aspect leads to simplified and specially condensedmeasuring apparatus. For instance, it is possibleby virtue of theinvention to place both theme-responsive resistance elements into asingle enclosure as shown in Fig. 2, rather than using two separatePirani-type elements for this purpose as has been necessary in In factany filament similar to those shown in Figures 1 thru 7 can be arrangedfor flow measurements by simply placing them axially parallel to thestream fiow and calibrating the instrument with known rates of fiow orby dividing into two halves placed and connected in a manner similar tothat explained for Fig. 8. The invention is adaptable to measurement ofvariations in the surroundingmedium such as ay be due to temperature,light intensity, mechanical or gas pressure, or changes in composition,in that a coating may be chosen whose resistance varies with changes inany or all of these conditions. I

While I have described in detail a limited number of embodiments inorder to exemplify the invention, it will be understood by those skilledin the art that the invention is not limited to those embodiments butmay also be carried out in various other ways without departing from theabove-mentioned objects and advantages and within the scope of theinvention as set forth in the appended claimb.

I claim: l 1. A gauge electrode subiect to variation in conductivity bythe character of the pressure of fluid medium surrounding the same andin contact therewith, comprising an insulative self-susi a film-likeelectrically conductive material on said body, said material forming acontinuous and highly resistive electrical path and changeable in itsresistance by effects of the pressure of fluid medium surrounding thesame and in contact therewith, and means for connecting a test circuitto said electrically conduc tive material at parts thereof electricallyremote from each other.

2. A gauge electrode subject to variation in conductivity by thecharacter of the pressure of fluid medium surrounding the same and incontact therewith, comprising an insulative self-susraining body oflarge surface area-compact within a small space, a film-likeelectrically conductive material on said surface area and establishing along and devious electrical path within said small'space, said materialbeing electrically re sistive and subject to heating by passage ofcurrent therethrough and having its resistance changed by change in thepressure of fluid me dium surrounding the same and in contact there=with, and. means for connecting a test circuit to said material at partsthereof electrically remote,

to each other along said devious electrical path. 3. A Pirani pressuregauge, comprising an en velope having duct means for supplying a gaspressure to be measured, a measuring conductor disposed in said envelopeto be exposed to said pressure, and leads passing through said envelopeto supply current from the outside to said conductor, said conductorhaving a heat-resistant insulating section and a conductive film dis-"posed on said section and connected with said leads.

4. A Pirani pressure gauge, comprising an envelope having duct meansfor'supplying a. gas pressure to be measured, a section of insulatingmaterial arranged in said envelope and having a plurality of adjacentportions so as to cover a surface area of multiple width as comparedwith that of a single section, a conductive coating of chemically inertmaterial deposited on said insulating section within the envelope whereexposed to the gas pressure from said duct, and leads passing throughsaid envelope and connected with said coating for supplying currentthereto.

5. A Pirani prewire gauge, comprising an envelope having duct means forsupplying a gas pressure to be measured, an insulating body of heatresistant material arranged in said envelope, a conductive coating ofchemically inert material deposited on said insulating body within theenvelope where exposed to the gas Dressure from said duct, and leadspassing through said envelope and connected with said coating forsupplying current thereto.

- URIE FUNAROFF.

